The subject matter disclosed herein relates generally to gamma ray detectors, and more particularly, to systems and methods for communicating signals in gamma ray detectors.
Gamma ray detectors may be used in different applications, such as in Positron Emission Tomography (PET) systems. PET systems perform nuclear medicine imaging that generates a three-dimensional image or picture of functional processes within a body. For example, a PET system generates images that represent the distribution of positron-emitting nuclides within the body of a patient. When a positron interacts with an electron by annihilation, the entire mass of the positron-electron pair is converted into two 511 keV photons. The photons are emitted in opposite directions along a line of response. The annihilation photons are detected by detectors that are placed along the line of response on a detector ring. When these photons arrive and are detected at the detector elements at the same time, this is referred to as coincidence. An image is then generated based on the acquired image data that includes the annihilation photon detection information.
In silicon photomultiplier based PET detectors, in order to cover a large area for detection of gamma rays, a large number of small area silicon photomultipliers (e.g., 3×3 mm2 or 4×4 mm2 photomultiplier devices) may be used. However, the large number of these photomultipliers increases the complexity of the devices, as well as the number of readout channels, which can result is higher cost and higher power requirements. For example, signals from a number of silicon photomultipliers may be added using multiplexing schemes. However, in order to provide input signal integrity, very low noise and high bandwidth amplifiers are used.
In order to reduce the number of channels, as well as the complexity of handling many small individual pixels (e.g., a one anode device or a one anode per pixel device), larger sized silicon photomultipliers may be used with different multiplexing schemes. The larger sized silicon photomultipliers reduce the number of signal channels that are processed. However, the total capacitance increases and stretches the tail of the signal pulses as the total capacitance is proportional to decay time. These stretched signal pulses have a lower amplitude and reduce the signal amplitude, thereby decreasing timing performance. Also, the larger the area, the more spread in the signal transit time from each microcell of a SiPM pixel is inevitable. This degrades the timing performance too.